The present invention relates to an apparatus for treating a liquid containing impurities in which intermittent operation of an airlift function for the transport of granular media to a granular media washer is provided.
In connection with many municipal and industrial water treatment systems, water/wastewater needs to be purified. One example can be a drinking water system in which drinking water is produced from surface water. Another example may be a municipal wastewater treatment system in which wastewater needs to be treated so that it can be discharged or reused for industrial, irrigational, or similar purposes.
Backwash upflow filters typically use airlifts in granular beds to stimulate the interaction between the granular beds and a liquid containing impurities to assist in separating the impurities from the liquid. Such filters typically do not have a device to detect and correct for the loss of airlift function. If the generated airlift stops lifting filter media, after a period of time the filter bed will become packed with impurities. Eventually, “break though” will occur which will release excessive amounts of impurities (such as solid, semi-solid, semi-liquid, or liquid contaminants, etc.) into the filtrate, thus creating unacceptable filtrate quality. The detection of airlift failures conventionally requires physical observation by an operator or administrator, and manual efforts to correct the situation. Unfortunately, airlift failures are often not noticed and corrected for hours or even days, and the corrective actions, such as removal and replacement of the airlift and/or the media bed or labor intensive air lancing of the bed, are required.
It is desired to provide a new and improved method and apparatus for the treatment of a liquid containing impurities, such as wastewater. For example, in the method and apparatus, the impurities and/or pollutants can be separated from the wastewater or other liquid in a granular media filter, such as a sand filter.